This invention relates to the use of isolators in connecting spacecraft payloads to a payload platform, in particular, using a launch locking device to restrain the payload and isolator during spacecraft launch.
So-called xe2x80x9claunch locksxe2x80x9d are called for in many isolated spacecraft payload applications primarily to confine stresses and the isolator stroke during the high g-force conditions that develop during a rocket launch. The isolators comprise a suspension spring and a fluid damper, designed to commonly resonate in the range of 2-10 Hz when supporting the payload. During launch quasi-static and random conditions can conceivably require the compliant isolators stroke between 1 and 20 inches just to prevent the payload from engaging the payload platform. Soft stops can be used as an alternative to launch locks, limiting isolator strokes but nevertheless produce additional shock forces to the payload platform and payload during the launch. Soft stops increase the complexity of the isolator design as well, for instance, in the design of damping elements and flexures for proper operation after launch.
Some locking mechanisms stiffly hold the payload in place by completely restraining the isolator and using bolt cutters, pyrotechnic bolts, separation nuts and Frangibolts to release the payload after launch. But these techniques only provide locking during the launch. None can re-lock the payload and isolator for an earth reentry.
A compliant member, such as coil spring or belleville spring stack, pulls on a pin clamping the payload against a launch lock housing. After the launch, a release shape memory alloy element is heated to overcome the compliant member, moving the pin away from the lock housing, releasing the payload. The element is substantially sized to hold this new size after the heat is removed.
An additional re-lock shape memory element may be heated, when the spacecraft is ready for reentry, to compress the release shape memory element and move the pin so that the payload is locked against the housing again. Both elements have sufficient cross-sectional area to hold their new sizes after the heat is removed from the re-lock shape memory element.